An aircraft gas turbine engine is typically equipped with a bearing lubrication system that supplies lubricant to various bearings that support rotating shafts. After flowing over the bearings, the oil collects in a sump provided at the bottom of the bearing housing. The oil may then flow from the sump into an oil tank, which holds a large reservoir of oil. Under the influence of a supply pump, the oil may then be drawn from the oil tank and supplied to the spray bar, which again directs the oil over the bearings. This cycle is continually repeated to maintain the bearings at a proper lubrication and operating temperature.
In some gas turbine engines, a bearing cavity exists within the bearing housing above the sump. In some of these same engines, it may be desirable to de-pressurize the bearing cavity to ensure certain seals remain energized, and thus prevent lubricant loss into the turbine gas path. It has been found, however, that in some systems, such de-pressurization is not needed at all operating conditions and at various altitudes above sea level. Such functionality could be implemented actively, but it could be potentially costly and complex.
Hence, there is a need for a passive device that will allow the engine bearing cavity of an aircraft gas turbine engine to be de-pressurized at relatively high throttle positions, while not de-pressurizing the cavity at relatively cruise positions and/or compensating for altitude variations. The present invention addresses at least this need.